diff --git a/server/index.js b/server/index.js
index e485ff4..30bff7e 100644
--- a/server/index.js
+++ b/server/index.js
@@ -47,6 +47,12 @@ function mountApp(base) {
 
   if (serveStatic) {
     app.use(prefix || '/', express.static(distDir));
+    // SPA fallback only for the app's base path, not root-level unknown files
+    app.get(`${prefix}/*`, (req, res, next) => {
+      const ext = req.path.split('.').pop();
+      if (ext && ext !== req.path) return next();
+      res.sendFile(path.join(distDir, 'index.html'));
+    });
   }
 }
 
@@ -57,6 +63,15 @@ if (SITE_BASE) {
   mountApp(SITE_BASE);
 }
 
+// Return proper 404 for missing static assets (prevents index.html served as JS/CSS)
+app.use((req, res, next) => {
+  const ext = req.path.split('.').pop();
+  if (ext && ext !== req.path) {
+    return res.status(404).json({ error: 'Not found' });
+  }
+  next();
+});
+
 app.use((err, _req, res, _next) => {
   if (err instanceof multer.MulterError && err.code === 'LIMIT_FILE_SIZE') {
     return res.status(413).json({ error: 'File too large (max 50MB)', code: 'FILE_TOO_LARGE' });